Picture of How to Make a Spot Welder - for Cheap!!
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Step 1: You Might Be Surprised How Cheap It Can Be

Picture of You Might Be Surprised How Cheap It Can Be
Have you seen the video above?  If not, take a look now because it will help you as you go along in this instructable. 

A typical resistance Spot-Welder can range in price from about $200-$800, but with a little resourcefulness, and a bit of free time, you can make one like this for about $10 or less.

Spot welders are used to fuse thin sheets of metal together.  They are most likely used in the auto industry, as well as HVAC for welding metal ducting.  

There are a couple of videos you should see before starting on this project, because you may want some background on how the device works.

Here is how to: Make The Metal Melter

Here is what it can do:  The Metal Melter

Step 2: Take Some Measurements

Picture of Take Some Measurements
Measuring the base of my Metal Melter, I found it was about 4-1/4".

I found a 6' length of 1x6 common board for about $4, which actually measures out at 5-1/2", so it will work just fine.

Two pieces of the board will need to be cut to 12" lengths (5-1/2" x 12"), but the rest can be pushed through a table saw to trim the width down to 4-1/2" (1/4" wider than the transformer base).

Step 3: Roughing The Case Together

Picture of Roughing The Case Together
The piece of common board that you just trimmed down to 4-1/2" wide can be cut into 3 pieces measuring;

  4"  x  4-1/2"
12"  x  4-1/2"
24"  x  4-1/2"

The other 2 pieces of the common board should measure;

12" x 5-1/2" (x 2 pieces)

You'll also need 4 pieces of 2x2 measuring;

2" x 2" x 13-1/2" (x 2 pieces)

2" x 2" x 4" (x 2 pieces)

This is all the wood you'll need for building the casing.

I used a 3/4" rounding bit and my router to smooth the edges and give it a cleaner look.  

This is roughly how it will look when it's assembled.

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Whatisthe thickest metal this will tolerate? Again, another fantastic write up sir.
Charles516 months ago

I put one of these contraptions together using your video as a guide and those of several others on YouTube. Melts wire amazingly. As an artist I need to spot weld wire together to form armatures. The wire gets red hot and will melt but it does not weld together and comes apart when additional pieces are added. Any idea why?

Sounds like too much resistance in the wire. Have you tried using bigger wire? Also keep the wire run from the transformer as short as possible.

Great instructable, Grant!

RobertP717 days ago

Hi, enjoy seeing what you have made. On the spot welder what wire are you using leading to the welding tips? 2/0 seems too stiff to have the arms removable or did I just miss something here?


Lots of projects I see I'm going to start doing in my retirement years!

fredF12 months ago

Are the transformer shunts left in or taken out?

The shunts are removed.

Anyone noticed we're trying to fit 6 inches of 2x2 into a 4.5 inches of space?

pnosko2 months ago

Let me ask a dumb question. You are using 1/4" hex screws to mount the terminal lugs to the arms. Considering that your metal melter videos show you melting similar screws, what is preventing these mounting screws from melting?

pnosko pnosko2 months ago

Answering my own question below after watching some educational electricity videos, I think the reason the 1/4" bolts are not affected is because the leads direct contact to the terminals make that the shortest path for the current, so it does not actually pass through the bolts.

Fission Chips3 months ago

Cool! I know this is dangerous to some extent, but exactly how dangerous is it?

felippec1 made it!4 months ago

I made it and work fine. thank you for inspiration.

Felippe Cardelino


SIRJAMES095 months ago

Sir, you never cease to amze me!

this is just too cool!!! :)

TY for sharing Sir.

stamatelos10 months ago

Thank you it is very usuful i will try to bild sun

I_StarkGuy made it!11 months ago

Finished mine! I changed the design to adapt it to available materials and I added the microwave fan to cool the MOT.

Can you weld galvanized steel? Mine is not able to do it, though my math gives me above 950 amps.


I think you can weld galvanized BUT the fumes given off are very toxic and potentially lethal. If you have to do this use a respirator, work outside or better yet, just try to avoid this if at all possible.

It is not that toxic in small quantities. And I work outside and I have been exposed to the fumes when melting screws.

The toxicity of galvanized metal when welded was one of the first lessons taught me by a pro. That said, just be careful (really, wear a respirator no matter where you are)!

JestGold11 months ago

Really like these projects and the metal melter/spot welder appear to be exactly what I need. Was wondering a couple of things:

a) I create metal sculptures from thin gauge wire rod and is there any way to regulate the amount of power so the metal fuses instead of melting (the spot welder seems to do just that)? and…

b) can the arms be separated or made into some sort of hand piece to make it more practical/accessible to the work?

Many thanks!

reddrexx1 year ago
I made one! But changed up the arms a bit. It works great.
14, 12:02 AM.jpg14, 12:02 AM.jpg
Are you sure you don't have AWG 2/0 wire ? It looks thicker than my AWG 2 wire. (2/0 is really 00 awg)
ccrow21 year ago
I have transformer from a die hard 6 and 12 volt battery charger I'm wondering how that would work, several input leads on the primary, the charger also had a 75 amp jump start setting also. Hmmm anybody wanna help me with where to start 6v 12v? I'd better do some math.
Pecheck1 year ago
late reply, but very awesome project. I'm definitely building one. I'll just ad a computer fan and some vent holes to by transformer housing.
kade1991 year ago
hey i was just wonder if for the MOT i should use the 2 AWG (since the 4 AWG melted) or if i should do the 8 gauge wire wrapped 16 times like in your arc welder video? which would be better overall for the spot welder?
I would think that if 8AWG wire wrapped 16 times worked better for the spot welder, then he probably would have said so, since they are both HIS videos ;-) But maybe he learned since making this one, and hasn't updated...
At any rate, 16 turns on the same core would result in higher voltage -- haven't watched the arc welder video yet -- guessing about 20V. Along with V increase, I (current, and resulting heat) goes down. I bet that the 2AWG (same number of turns) is the way to go here, since heating will occur in the secondary AND the work. I think the idea is to get the high current for the heat, and just make sure not to try melting anything that melts easier than the secondary's insulation! Assuming insulation was no issue, you'd simply have to keep the work easier to melt than the secondary itself, which is probably a complex relationship between relative masses and melting points.

But now I'm gonna have to go watch the arc welder video... are those capacitors I smell? :-)
GraphixS61 year ago
Do you know any place that you can reliably get dead microwaves. It seems my neighbors don't have a habit of just throwing them out.
f.masoni1 year ago
I love this project, i want to make one of my own but have a couple of questions.

Where i live the voltage of a power outlet is 220v does this change anything?

Also is it possible to make one that welds two separate spots at once with the same transformer.

Best Regards
calebwang1 year ago
I love your project. Your video editing is top notch as well.
The King of Random (author)  calebwang1 year ago
Thank you! Thank you!
Hi there. Thanks for this amazing project! I was amazed how easy it was to make. Luckily when I discovered this project, I knew were an old microwave was. I live in a small village in Guyana and most people here don't have microwaves. It was from a small restaurant. I successfully got the transformer out which was a little scary even for a 16 year old. I built a deluxe version of your design with the microwave light and fan incorporated in, along with four switches. My problem was that I didn't have any solid copper rod to use for the contacts. I had a few bronze welding rods so I used a small piece of that, instead. My welder is putting out about 1v. It melts nails and about anything else. I have not gotten it to actually weld. The metal to weld gets red hot but doesn't weld together. Any idea's whats wrong? I would appreciate any help. It's fun to melt metal, but it doesn't weld. Thanks.
Thanks for your comment! I'd love to see a little video of your welder as a video response to my video on YouTube, if you get a chance to do that?

It may help to press the contacts together harder when welding. You may also need more power. (Eg. Bigger transformer)
swolff12341 year ago
Yes, I am actually a ham. I got my license in Jan. No radio yet, but I have Echolink. I am getting my radio in March. Are you a ham? Thanks for all your help! BTW, the reply feature isn't working for me, I can only post new comments.
Sam Wolff KK4NVJ
The King of Random (author)  swolff12341 year ago
Awesome! I did get licensed but haven't ever done anything with it. I'm hoping that one day I can explore that world a little more :)
swolff12341 year ago
Found it! It was hiding from me..... Lol. Thanks again! Oh, how long does the trasformer last until the insulation on the 4 awg melts?
Best of luck,

Sam Wolff
The King of Random (author)  swolff12341 year ago
Hey, are you a Ham by chance?

If you use the transformer in short bursts of 10 seconds or less, you should be able to use it indefinitely. Allow time to cool in-between. You'll be able to tell the wires are starting to melt because they will be smoking. So stop when you see smoke (or before) and it should last forever.
swolff12341 year ago
Thank you for the quick response. I have asked questions on other instructables on my old account about 3 years ago and still have not received an answer.
Do you remember what hardware store? I went to Home Depot and could not find it.
The King of Random (author)  swolff12341 year ago
It was Home Depot in the wire cutting area. All the best!
swolff12341 year ago
I also have a suggestion. When i built mine, I could not find a nail long enough for the pivot point. So I took a coat-hanger sized steel rod, and drilled a hole straight through the box and arm. I then bent the sides of the rod after I had fed the rod through the holes. I then found the nails. I compared the two pivot systems. I was amazed at how well mine worked.
The King of Random (author)  swolff12341 year ago
Excellent suggestion. Thank you!
swolff12341 year ago
First off, THANK YOU FOR THIS! I have been looking for something like this forever! Also, I don't have the solid copper wire, but I do have the same sized aluminum wire and I have stranded copper. Can I use the stranded and just twist it? And can i use the aluminum? Lastly, how much is the solid copper wire you are using and where can I get it?
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